Stop Over-Specifying: The Engineering Reality of H1 Reports in New Zealand

Meeting the updated 2026 H1 Building Code requirements (6th Edition) is causing a lot of unnecessary panic in the New Zealand construction industry. As engineering consultants specialising in performance-led design, we are seeing a recurring theme: architects and builders assuming they have to drastically alter their standard construction methods, add massive costs, and over-specify materials just to comply.

This article strips away the theory and focuses on the engineering reality of H1 compliance—because the truth is, if you approach it correctly, it is largely business as usual.

The 38% Framing Trap: You Probably Don't Need 140mm Walls

The biggest misconception we see right now revolves around the new 35% framing percentage rules in H1/AS1 and VM1.

"for framed walls, a wall framing fraction of no less than 38% shall be assumed unless it can be demonstrated that a lower wall framing fraction is appropriate for the building" - H1/VM1 - 6th edition, 2.1.2.1.a.i

When looking strictly at the calculation method, many designers panic. They look at the new reference building targets and assume their only options are to upgrade to 140mm framing, or stick with a 90mm wall and double-strap it with 45mm or 70mm battens just to cram in the extra insulation.

This is a costly trap. 

The calculation method is rigid and punishing. However, when we switch to the modelling method, the software takes into account the holistic performance of the entire building envelope.

By looking at the bigger picture—how the whole building actually performs rather than isolating a single wall—we routinely prove that standard 90mm framing is still perfectly compliant for many projects.

Case Study: Avoiding "Overkill" in Climate Zone 5

We recently consulted on a 5-unit townhouse project in the demanding climate of Zone 5.

The client came to us operating under the assumption that they were going to have to heavily strap their walls to accommodate extra-high insulation to meet the new targets. It threatened to eat into their floor plan and their budget.

We took their design into our simulation software. The reality? The townhouse block was actually incredibly well-balanced thermally. By analysing the building as a complete system, we proved there was absolutely no need for overkill strapping. We achieved full compliance while keeping the wall profiles lean and cost-effective.

Don't Sacrifice Your Windows

Another dangerous assumption we are seeing in 2026 is that you must aggressively limit your glazing area—often restricting designs to sub-40% glazing—or rely on heavily tinted, hyper-expensive glass just to comply.

If you are starting a new project, do not limit the number of windows or assume what type of glazing you need before doing the math. You do not need to turn your building into a dark cave to pass H1.

By utilising the modelling method, we can balance out larger glazing areas against the thermal mass and insulation of the rest of the building. Unlike the basic H1/AS1 calculation methods, dynamic modelling actually accounts for external factors like eaves, overhangs, and even neighbouring buildings. These elements dictate exactly how light and heat enter the space, which has a massive impact on the final thermal results.

If you are utilising really large eaves or overhangs to manage solar gain (say over 2m), council may need you to prove the interior receives adequate natural light as per G7.

Because we build a comprehensive 3D model for the H1 report, we can use that exact same model to run a dedicated G7/VM1 daylighting analysis. This integrated approach guarantees your building complies with both thermal H1 and natural light G7 requirements, preserving your architectural intent without duplicating the modelling costs.

Our Methodology: Proof Over Guesswork

We don't guess at compliance, and we don't rely on basic calculators. Our modelling is rigorous, defensible, and designed to stand up to any Building Consent Authority (BCA).

By taking your initial architectural geometry—often straight off the PDF architectural plans —we run the calculations using EnergyPlus™ v22.2, the industry-leading simulation engine developed and maintained by the U.S. Department of Energy. All of our calculations are tested in strict accordance with ASHRAE Standard 140 (Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs) and utilise all applicable H1 equations to represent an accurate, Acceptable Solution under Section 22(1) of the Building Act 2004.

The Golden Rule: When to Engage the Engineer

If there is one piece of advice we give to architects and developers for their H1 Reports, it is this: Do not make assumptions, and bring us in at the "Sweet Spot."

The best time to come to us is when you know your general build-ups and spatial layouts, but before you have locked in the fine construction details. If you engage us at this specific stage, we can usually:

• Bring assumed 140mm walls back down to standard 90mm.

• Remove the need for oversized rafters.

• Eliminate the need to raise roof heel heights just to wedge in unnecessary insulation.

• Remove slab edge insulation.

• Look at whether non thermally broken window frames are right for your project.

You will be surprised by what the modelling method can achieve. Practical, performance-led engineering is about finding the smartest path to compliance—not the thickest one.

Frequently Asked Questions (FAQ)

What information do you actually need from us to start an H1 model?

To get started, all we need is a PDF showing your elevations, sections, floor plans, and a window and door schedule. It is ideal if you have your specific construction build-ups (like roof and wall profiles) ready, but if you don't, we can make industry-standard assumptions to get the model running during your detailed concept stage. Once your design is finalised, all of our H1 reports come with at least one free opportunity to update the report with any final changes.

For H1 6th edition, will I be forced to install an expensive mechanical ventilation (MVHR) system?

No, you are not strictly forced to install mechanical ventilation to pass. However, because new buildings are built to a much higher quality and airtightness standards, condensation is a major risk. The reality is that most occupants do not open their windows for the recommended length of time each day to naturally ventilate the space. This is especially true for smaller floor plans or rental properties. We can recommend highly cost-effective HVAC options that keep condensation to a minimum and protect occupant health, without blowing out your build budget.

How does the modelling method handle thermal bridging for steel-framed houses?

If you are designing a steel-framed house, we definitely need to calculate the thermal bridging to accurately model the heat loss through the envelope. It is a critical part of the compliance model for steel structures. Please note, however, that while we calculate this thermal bridging to ensure H1 compliance, we won't be doing anything to look at condensation within your house as part of that specific process. If you want a condensation anaylsis done, you can find out more here.

Will using the modelling method delay my building consent or force late design changes?

Usually, it only takes three to five working days to get an H1 report back to you. If you have an urgent deadline, we can make it happen faster. Obviously, the sooner you get the plans to us during the building design process, the more flexibility you have.

However, even if you come to us late in the process, we almost never have to tell clients to reduce their glazing area or increase their framing size. The worst-case scenario is usually just tweaking the R-value of your insulation or adjusting the specific type of glazing.

The Bottom Line: Your H1 Report Doesn't Have to Compromise Design

The 6th Edition H1 updates represent a significant shift in New Zealand's building standards, but they do not have to dictate your architecture or blow out your construction budgets. The panic currently echoing through the industry is largely driven by the limitations of the basic calculation method.

By using the H1/VM1 modelling compliance pathway, you regain control of your project. Whether it is proving standard 90mm framing still works, saving your expansive glazing, or avoiding overkill strapping in harsh climates, the data speaks for itself.

Don't let the rigid H1/AS1 calculation method force you into expensive, over-engineered solutions. If you have a project on the drawing board, reach out to us during your detailed concept stage. Let us handle the H1, daylighting, and condensation modelling so you can focus on what you do best—designing and building great spaces.